code: def expected_mean(merged_shapes):
      test_mean = merged_shapes.copy()
      test_mean["BoroCode"] = [4, 1.5]
      return test_mean
  
imports: import warnings
  import numpy
  import pandas
  import geopandas
  from geopandas import GeoDataFrame, read_file
  from pandas.testing import assert_frame_equal
  import pytest
  from geopandas._compat import PANDAS_GE_15, PANDAS_GE_20
  from geopandas.testing import assert_geodataframe_equal, geom_almost_equals
label_desc: Use image node_id 4 for calling a global function with example usage: expected_mean(merged_shapes) and returns: test_mean